1. Field of the Invention
The present invention relates to methods of controlling an electrostatic chuck used in the fabrication of semiconductors, and more particularly, to methods for restoring an electrostatic chuck force of an electrostatic chuck.
2. Background of the Related Art
In general, mechanical clamps have been used for holding a wafer in semiconductor fabricating equipment. However, it is a current trend to use an electrostatic chuck, which provides greater process uniformity. Use of electrostatic chucks has been sharply increasing, particularly for high density plasma etching and deposition processes. However, the electrostatic chuck has a problem in that the deposition of particles and polymers on the chuck, which occurs during use of the chuck, causes a back side Helium(He) flow. In addition, charges can accumulate on the chuck when a large Radio Frequency (RF) bias power is applied to a wafer during processing, or during a prolonged series of process steps. The accumulated charge reduces the chuck's electrostatic holding force during subsequent process steps. Though the back side He flow can be eliminated by periodic cleaning of the chuck, it is difficult to eliminate the charge buildup that occurs as process steps are performed.
A conventional electrostatic chuck will be explained with reference to FIG. 1. The conventional electrostatic chuck includes a base plate 2, a ceramic plate 3 and an aluminum plate 4 disposed in succession under a chuck 11 with a focus ring 1. The chuck also includes a power source 9 for inducing a chucking voltage in the chuck 11 and a filter 8 connected between the power source 9 and the chuck 11. A Radio Frequency (RF) generating part 7, a RF matching circuit network 6 and a RF rod 5 are connected in series for supplying RF power to the chuck 11. The chuck 11, base plate 2, ceramic plate 3 and aluminum plate 4 are included in a puck part 10.
As has been explained, the conventional electrostatic chuck may have a significant problem with high back side He flow and charge accumulation. These problems impede restoration of a sufficient chuck force in subsequent process steps. To cope with this problem, either the reaction chamber of the processing equipment is vented to clean the chuck 11 between processing steps, or the polarity of the chuck 11 is manually changed to remove accumulated charges. The venting step, or the polarity reversal step, however, make the fabrication process more expensive and time consuming. Also, automatically or manually performing a polarity reversal step causes trouble in the fabrication process due to modification of the plasma apparatus, and an attempt to manually remove the charge cannot completely remove charges in the chuck.
To summarize, the conventional methods for restoring an electrostatic chuck force have various problems. For example, venting the reaction chamber to clean the chuck between fabricating process steps causes losses of time and money. Further, changing the electrode polarities of the electrostatic chuck cannot completely discharge an accumulated charge, and it requires partly modifying the apparatus.